Wet abatemenbt system for waste SiH4

ABSTRACT

A new method of silane abatement is achieved. The novel silane abatement system comprises a water-filled chamber within an outer chamber. An air intake is located in one upper portion of said outer chamber and an exhaust output is located in another upper portion of the outer chamber. A silane gas intake pipe runs into the outer chamber and has its output under water in the water-filled chamber. A drain is connected through a valve at a bottom portion of the water-filled chamber. Many safety features are built into the wet abatement system, including temperature and water level sensors, water sprinklers, and means for shutting off air supply, exhaust, and silane intake. Waste silane gas is bubbled into a water-filled chamber. The waste silane gas is reacted with oxygen in water in the water-filled chamber whereby SiO 2  precipitates are formed and wherein the SiO 2  precipitates settle to a bottom surface of the water-filled chamber. The SiO 2  precipitates are drained out of the water-filled chamber to complete the abatement process.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method of and device for abatement of wasteSiH₄ in the fabrication of integrated circuits, and more particularly,to a method of and device for safe wet abatement of waste SiH₄ in themanufacture of integrated circuits.

2. Description of the Prior Art

Chemical vapor deposition (CVD) processes are widely used in integratedcircuit manufacturing. For example, polysilicon or silicon dioxidelayers can be deposited by CVD using silane (SiH₄) gas or other similargases. After the CVD process has been completed, excess silane gasremains in the CVD system. Typically, excess reactant gases are removedby an exhaust system. The exhaust system may vent the reactant gas tothe atmosphere. However, silane gas is pyrophoric and cannot be releasedinto the atmosphere. Silanes and similar gases must be filtered from theexhaust gas stream or converted to compounds that can be disposed ofsafely. A common method of converting waste silane to a disposablecompound is through combustion in a so-called “burn box”. In the burnbox, the SiH₄ is converted to SiO₂ by the reaction: 2SiH₄+2O₂→2SiO₂+4H₂.However, the risk is that the burn box may be a source of fire if systemfailure occurs suddenly. For example, if the exhaust system fails,residue SiH₄ will collect in the burn box making it likely that anuncontrolled fire will start.

U.S. Pat. Nos. 6,174,349 to DeSantis, 6,126,906 to Imamura, and5,183,646 to Anderson et al describe processes and devices includingburn boxes. Wet scrubbers and other abatement methods are also used.U.S. Pat. No. 6,174,349 to DeSantis teaches a wet scrubber incombination with the burn box. U.S. Pat. No. 5,955,037 to Holst et alshows an oxidation treatment. U.S. Pat. No. 5,320,817 to Hardwick et aluses an amine-forming metal salt to scrub silane.

SUMMARY OF THE INVENTION

Accordingly, a principal object of the present invention is to providean effective and very manufacturable method of silane abatement in thefabrication of integrated circuit devices.

Another object of the present invention is to provide an effective andvery manufacturable method of silane abatement wherein the abatementsystem does not present the danger of being a source of fire.

Another object of the invention is to provide a silane abatement systemthat does not present the danger of being the source of fire.

In accordance with the objects of this invention a new method of silaneabatement is achieved. Waste silane gas is bubbled into a water-filledchamber. The waste silane gas is reacted with oxygen in water in thewater-filled chamber whereby SiO₂ precipitates are formed and whereinthe SiO₂ precipitates settle to a bottom surface of the water-filledchamber. The SiO₂ precipitates are drained out of the water-filledchamber to complete the abatement process.

Also in accordance with the objects of this invention a new silaneabatement system is achieved. The silane abatement system comprises awater-filled chamber within an outer chamber. An air intake is locatedin one upper portion of the outer chamber and an exhaust output islocated in another upper portion of the outer chamber. A silane gasintake pipe runs into the outer chamber and has its output under waterin the water-filled chamber. A drain is connected through a valve at abottom portion of the water-filled chamber. Many safety features arebuilt into the wet abatement system, including temperature and waterlevel sensors, water sprinklers, and means for shutting off air supply,exhaust, and silane intake.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings forming a material part of thisdescription, there is shown:

FIGS. 1 and 2 schematically illustrate in cross-sectional representationa preferred embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a method and a device for waste silaneabatement. The waste silane abatement system of the present inventionsuccessfully deals with the waste silane without danger of being a firesource. No burn box is used in the method and-device of the invention.Rather, waste SiH₄ gas is reacted with dissolved oxygen to form solidSiO₂ which can be disposed of safely. Safety features of the device ofthe present invention include sprinklers that will be automaticallytriggered in the event of fire.

FIGS. 1 and 2 illustrate the waste SiH₄ abatement system of the presentinvention. Referring now to FIG. 1, waste abatement device 10 is shown.A portion of the device is filled with water 22. Oxygen gas is dissolvedin the water 22. Waste SiH₄ gas enters the chamber 10 from through apressurized pipe 18. High pressure N₂ gas flow 19 pushes the SiH₄ gasthrough the pipe 18, into the chamber 10 and out through the pipe 24under the water. N₂ gas here is used to prevent back fire to the processtool. If backfire occurs, N₂ is activated to push the fire into thewater chamber. The N₂ gas flow is at a high pressure of about 100 psi.

The SiH₄ gas is bubbled into the water 22. FIG. 2 is a close-up of thepipe 24. The waste SiH4 gas is pumped through pipe 18 into a C-shapedstainless steel square pipe 24. Flippers 14 are pushed upward bypressure to release SiH₄ gas for reaction with dissolved O₂ forabatement. In water at 25° C., there is about 8.4 ppm of dissolved O₂.The gas reacts with dissolved oxygen in the water to form a heavyprecipitate of SiO₂. The SiO₂ precipitate sinks slowly to the base ofthe chamber. The drain valve 26 is opened, subject to the SiO₂ level, toclear the solid SiO₂ out through the drain 28. Most likely, the drainvalve may be opened once a day.

Chamber 20 provides for water overflow. Continuous fresh air intake 30into the chamber 10 insures the process of oxygen dissolving into thewater from the air is not interrupted. An open-ended drain 36 in thechamber 20 will capture water over-flow from the water-filled section 22of the chamber. An exhaust pipe 38 is separated from the chamber 10 byan exhaust flipper 32. The exothermic abatement process may releasesmoke into the chamber. This smoke is exhausted into the pipe 38. Theexhaust pipe also provides forced air ventilation from the chamberoutside into chamber 10 for the air dissolving process.

A controller 34 controls the water supply 42 and fusible link 44. Thecontroller also monitors a water temperature sensor 46, a water levelsensor 48, and an exhaust temperature sensor 50. Water sprinklers 52located in the chamber ceiling and in the exhaust pipe are triggered bythe controller by a high water temperature, high exhaust pipetemperature, or when the fusible link is broken. The fusible link is aburnable material such as nylon. If this link is exposed to heat highenough to break it, the controller will turn on the water sprinklers.The water level sensor avoids “dry-run” operations if the water level isnot high enough.

If a minor explosion occurs within the chamber 10, the air intake 30 andthe exhaust flipper 32 will shut. The flippers are normally open, butwill be pushed closed by the pressure of an explosion. The oxygen sourcewill also be cut off to stop any fire. That is, the air intake flipper30, normally open, will be pushed closed by pressure due to fire. If thefusible link 49 within one or both of the N2 high pressure pipes isbroken, indicating high heat, high pressure N₂ flow 19 will be triggeredto push the fire back into the water chamber 22 and to form N₂blanketing to stop a fire.

The wet abatement system of the present invention consists of awater-filled chamber within an outer chamber. An air intake flipper andan exhaust flipper control input and output of air. A drain is connectedthrough a valve to the water-filled chamber. An overflow drain is at thebottom of the outer chamber. A controller controls the water supply andmonitors the water level, water temperature, exhaust temperature,. and afusible link within the exhaust pipe. A pipe brings waste SiH₄ gas intothe water-filled chamber. A high pressure pump pushes the waste gasthrough the pipe.

In the wet abatement process of the present invention, waste silane gasis bubbled into the water-filled chamber of the wet abatement system ofthe present invention. N₂ gas at high pressure pushes the silane gasthrough a pipe into the water-filled chamber. The silane gas reacts withoxygen dissolved in the water to form a precipitate of SiO₂. The SiO₂settles to the bottom of the chamber and is removed from the chamberthrough a drain.

The process of the present invention abates waste SiH₄ in the waterstate. The abatement system will not be a source of fire because of thesafety features of the wet abatement system of the present invention.These safety features include: water sprinklers located on the ceilingof the outer chamber above the water-filled chamber and in the exhaustpipe, air intake and exhaust flippers that close in the event of anexplosion, a process pump trip, fusible links located within the exhaustpipe and within the N2 pipes that will break if exposed to high heat,water temperature and exhaust temperature sensors, and a water levelsensor. The controller monitors the sensors and the fusible links. Ifeither of the temperature sensors show a high temperature or if any ofthe fusible links are broken, the water sprinklers are triggered, theair intake and exhaust flippers are closed, the oxygen supply into thechamber is cut off, and the N₂ gas pump is shut down after pushingresidue waste gas into the water-filled chamber. If the water levelsensor shows the water level is too low, the system is also shut down.

The process and device of the present invention provide wet silaneabatement without danger of fire from the abatement system. The wetabatement system of the present invention has a variety of safetyfeatures that work together to provide safe and effective silaneabatement.

While the invention has been particularly shown and described withreference to the preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade without departing from the spirit and scope of the invention.

What is claimed is:

1. A silane abatement system comprising: a water-filled chamber withinan outer chamber; an air intake in one upper portion of said outerchamber; an exhaust output in another upper portion of said outerchamber; a silane gas intake pipe running into said outer chamber andhaving its output under water in said water-filled chamber; and a drainconnected through a valve at a bottom portion of said water-filledchamber.
 2. The silane abatement system according to claim 1 whereinsaid output of said silane gas intake pipe is into a C-shaped stainlesssteel pipe having upwardly opening flippers whereby silane gas isreleased into water within said water-filled chamber.
 3. The silaneabatement system according to claim 1 wherein said air intake and saidexhaust output both comprise inwardly opening flippers.
 4. The silaneabatement system according to claim 1 further comprising an overflowdrain at a bottom portion of said outer chamber.
 5. The silane abatementsystem according to claim 1 further comprising: a water supply pipeconnected to said water-filled chamber; a water level sensor connectedto said water-filled chamber; and a water temperature sensor connectedto said water-filled chamber.
 6. The silane abatement system accordingto claim 5 further comprising a controller that controls said watersupply and monitors said water level sensor and said water temperaturesensor.
 7. The silane abatement system according to claim 6 wherein inthe event that said controller detects an unacceptable condition fromeither of said water level sensor or said water temperature sensor, saidair intake and said exhaust output are closed, and residue waste silanegas within said silane gas intake pipe is pumped into said water-filledchamber.
 8. The silane abatement system according to claim 1 furthercomprising: an exhaust pipe exiting said outer chamber through saidexhaust output; an exhaust temperature sensor connected to said exhaustpipe; and a fusible link within said exhaust pipe.
 9. The silaneabatement system according to claim 8 wherein in the event that anunacceptable condition is detected in either of said exhaust temperaturesensor or said fusible link, said air intake and said exhaust output areclosed, and residue waste silane gas within said silane gas intake pipeis pumped into said water-filled chamber.
 10. The silane abatementsystem according to claim 1 further comprising a high pressure pumpconnected to said silane gas intake pipe.
 11. The silane abatementsystem according to claim 10 wherein said high pressure pump provides N₂gas for pushing silane gas through said gas intake pipe into saidwater-filled chamber.
 12. The silane abatement system according to claim1 further comprising a fusible link within said high pressure pump. 13.The silane abatement system according to claim 1 further comprisingwater sprinklers on an upper portion of said outer chamber and over saidwater-filled chamber.
 14. The silane abatement system according to claim1 further comprising water sprinklers on surfaces of said exhaust pipe.15. The silane abatement system according to claim 1 wherein wastesilane gas is abated by: bubbling silane gas through said silane gasintake pipe and into said water-filled chamber; reacting said silane gaswith oxygen dissolved in water in said water-filled chamber whereby SiO₂precipitates are formed and wherein said SiO₂ precipitates settle to abottom surface of said water-filled chamber; and opening said valve todrain said SiO₂ precipitates out of said water-filled chamber throughsaid drain. 16-17. (canceled)
 18. A silane abatement system comprising:a water-filled chamber within an outer chamber; an air intake in oneupper portion of said outer chamber; an exhaust output in another upperportion of said outer chamber connecting to an exhaust pipe; watersprinklers on an upper portion of said outer chamber and over saidwater-filled chamber and on surfaces of said exhaust pipe; a silane gasintake pipe running into said outer chamber and having its output underwater in said water-filled chamber; and a drain connected through avalve at a bottom portion of said water-filled chamber.
 19. The silaneabatement system according to claim 18 wherein said output of saidsilane gas intake pipe is into a C-shaped stainless steel pipe havingupwardly opening flippers whereby silane gas is released into waterwithin said water-filled chamber.
 20. The silane abatement systemaccording to claim 18 wherein said air intake and said exhaust outputboth comprise inwardly opening flippers.
 21. The silane abatement systemaccording to claim 18 further comprising an overflow drain at a bottomportion of said outer chamber.
 22. The silane abatement system accordingto claim 18 further comprising: a water supply pipe connected to saidwater-filled chamber; a water level sensor connected to saidwater-filled chamber; a water temperature sensor connected to saidwater-filled chamber; an exhaust temperature sensor connected to saidexhaust pipe; a fusible link within said exhaust pipe; and a controllerthat controls said water supply and monitors said water level sensor,said water temperature sensor, said exhaust temperature sensor, and saidfusible link.
 23. The silane abatement system according to claim 18further comprising a high pressure pump connected to said silane gasintake pipe having a fusible link within said high pressure pump. 24.The silane abatement system according to claim 18 wherein waste silanegas is abated by: bubbling silane gas through said silane gas intakepipe and into said water-filled chamber; reacting said silane gas withoxygen in water in said water-filled chamber whereby SiO₂ precipitatesare formed and wherein said SiO₂ precipitates settle to a bottom surfaceof said water-filled chamber; and opening said valve to drain said SiO₂precipitates out of said water-filled chamber through said drain. 25.The silane abatement system according to claim 22 wherein in the eventthat said controller detects an unacceptable condition from any of saidwater level sensor, said water temperature sensor, said exhausttemperature sensor, or said fusible link, said water sprinklers aretriggered, said air intake and exhaust flippers are closed, and residuewaste silane gas within said silane gas intake pipe is pumped into saidwater-filled chamber.
 26. A silane abatement system comprising: awater-filled chamber within an outer chamber; an air intake in one upperportion of said outer chamber; and a silane gas intake pipe running intosaid outer chamber and having its output under water in saidwater-filled chamber.
 27. The silane abatement system according to claim26 wherein waste silane gas is abated by: flowing N₂ gas at highpressure to push waste silane gas through said silane gas intake pipeinto said water-filled chamber; reacting said silane gas with oxygendissolved in water in said water-filled chamber whereby SiO₂precipitates are formed and wherein said SiO₂ precipitates settle to abottom surface of said water-filled chamber; and draining said SiO₂precipitates out of said water-filled chamber. surface of saidwater-filled chamber; and draining said SiO₂ precipitates out of saidwater-filled chamber.